When we think of animal migrations, perhaps we picture a huge herd of wildebeest, flutter of monarch butterflies or flock of shearwaters travelling en masse. In our river systems, species also migrate – sometimes together, sometimes solo, and often unseen.
Why does a creature need to migrate in a river? Some of the inhabitants of the Wirribi Yaluk/Werribee River must move to different parts for spawning, to seek food, or to disperse as adults. Eels migrate as tiny elvers from the ocean, to the river to grow, and then back to saltwater as they make their epic migration to the Coral Sea to breed. Little galaxia fish swim to the lower part of the river to lay their eggs. Their young drift out of the estuary and spend the first six months of their lives in the sea before returning. Platypus move away from the area of river where they are born to find their own territory. Male platypus have been found to travel up to 45km to establish their own home range, and some may travel even further (1). There are around 30 species of fish found throughout the Wirribi Yaluk/Werribee River, and most freshwater native fish are migratory at some stage during their life cycles. These include common galaxias, short-finned eel, tupong and Australian smelt.
Traditional Owners in Australia made use of this movement of fish along waterways as a food resource for many thousands of years (2). They engineered a range of ethnotechnologies including weirs, channels and traps to collect fish as they travelled in the river current (3). This allowed for sustainable and selective harvesting while non-target species could continue to travel unimpeded.
Since European arrival, the river landscape has changed. Solid dams and weirs were built to store and divert water, to irrigate the land and supply water to homes and businesses. Water resources are essential to support our lifestyles and food production but they have altered the ecological function of the river. The largest dam on Wirribi Yaluk/Werribee River is the Melton Reservoir, which holds a capacity of 14,364ML with a dam wall over 35m in height (4). This barrier effectively divides the river into two sections as no river creatures can move back and forth across it.
Smaller structures like the Werribee Diversion Weir at Riverbend Historical Park are less of an obstacle to creatures like eels and platypus, who can crawl up the sloping wall. This weir was completed in 1912 and diverts water to the farmland at Werribee South, managed by Southern Rural Water (5). If you visit this stretch of the river regularly, you may notice that sometimes there is a greater volume of water flowing over the top of the weir. Outside of flood events, this is often due to an environmental water release.
Over millions of years, as the river wound across the plains, the volume of water would rise and fall with the seasons. During times of higher rainfall, waterways would overflow and spill into wetlands and surrounding floodplains. With regulation of the river, these events happen less frequently, causing some wetlands to dry out and be lost. With changes in our approach to water and land management, water is now released from reservoirs to provide flow to the river when water levels get low, or to mimic those historical seasonal flows. This has happened in the Wirribi Yaluk/Werribee River since 2011, and is managed by Melbourne Water (6).
Water releases can help fish migrations by allowing them to move upstream. But how do they navigate the water velocity and river obstacles? Galaxia fish are only around 10cm long as adults. This is where fish ladders come in. Although they sound like something you’d find in the aisle with tartan paint and sky hooks, they’re actually a clever bit of engineering, allowing fish to travel up and around these human-made structures to get to the locations they need to.
Fish ladders, or fishways, are often made of natural materials such as rocks, and come in a wide variety of designs (7). They all enable fish to travel around an obstacle which might prevent their passage for migration, and aid in their long-term survival (8). There are two fishways already in the river – at the Bluestone Ford below Werribee Mansion (pictured above), and at Cobbledicks Ford west of Tarneit. These are rock ramps, which resemble natural structures and form pools in between the rock ridges. This allows fish to rest in between leaping or swimming against the current. The large rocks create little eddies behind them, making it easier for small fish to make their way upstream, and also resist movement when the river is in flood.
There are now plans in development for a Lower Diversion Weir Fishway, to help fish to migrate around this barrier. The Diversion Weir is adjacent to the site of the future Werribee Township Regional Park, managed by Parks Victoria (9). The park is located on Wadawurrung Country on the western side of the river and the fishway may be included as a feature of the park. The project is being designed by Melbourne Water in consultation with Bunurong, Wadawurrung and Wurundjeri Woi-Wurrung Traditional Owners, Southern Rural Water and other stakeholders. The planning process includes input from fish ecologists, surveys, and analysis of how different design features will best fit the needs of local species and the location.
Rivers are no longer seen as merely a resource that can be harnessed for human purposes. In the landmark New Zealand case Te Awa Tupua in 2014, the Whanganui River was recognised as a person, with its own legal personality and rights (10). This perspective helps to guide management of natural features and ecosystems by understanding the needs of the river community, and the river itself. In Australia, the cultural and scientific knowledge held by First Nations Peoples around water management is integral to ensuring a future of healthy waterways and Country (11).
When you next visit your local creek or waterway, there might be a migration happening just beneath the surface. As we continue to work together to make these places healthier, by removing barriers, regenerating degraded areas, and supporting river creatures, the life of the river returns. By enabling more native fish to make their journeys up and down the river, we can help to restore biodiversity and connection between communities, including our own.
Links:
- Platypus home range, movements and dispersal – Australian Platypus Conservancy
- Budj Bim Cultural Landscape | National Museum of Australia (nma.gov.au)
- Indigenous fish traps and fish weirs on the Darling (Baaka) River, south‐eastern Australia, and their influence on the ecology and morphology of the river and floodplains – Martin – 2023 – Archaeology in Oceania – Wiley Online Library
- Melton Reservoir | Southern Rural Water (srw.com.au)
- Werribee Irrigation District | Southern Rural Water (srw.com.au)
- Environmental water release for Werribee River | Melbourne Water
- 7 Types of Fish Ladders or Fishways – The Constructor
- Navigating fish highways in North Queensland | OzFish Unlimited
- Werribee Township Regional Park (parks.vic.gov.au)
- Te Awa Tupua (tpk.govt.nz)
- Indigenous water | Australia state of the environment 2021 (dcceew.gov.au
Image: Fish ladder at Bluestone Ford, Werribee River. Photo: C. Williamson (2023)